1. Field of the Invention
The present invention relates to a novel thermoplastic resin composition which can be made into molded articles by injection molding, extrusion molding, or the like.
2. Related Art
Polyphenylene ether is a resin which is generally superior in heat resistance, hot water resistance, dimensional stability, and mechanical and electrical properties. On the other hand, it suffers from the disadvantage of having poor moldability (due to high melt viscosity), low chemical resistance, and low impact resistance.
It is known that polyphenylene ether will have improved moldability without any adverse effect on its superior characteristics when it is decreased in melt viscosity by the incorporation of a polystyrene resin. However, the resulting composition is still poor in chemical resistance.
It is disclosed in U.S. Pat. No. 4189411 and UK Patent No. 1344729 that a polyphenylene ether resin composition will have improved processability when it is decreased in molding temperature and melt viscosity by the incorporation of a low-molecular weight hydrocarbon resin.
Also, Japanese Patent Laid-open No. 118956/1980 discloses the incorporation of a petroleum-derived low-molecular weight resin or rosin resin into a polyphenylene ether resin composition for the reduction of its melt viscosity.
Japanese Patent Publication No. 13584/1982 discloses a method of decreasing the melt viscosity of polyphenylene ether by incorporation with an aromatic hydrocarbon resin derived from cracked naphtha.
Although the above-cited inventions are intended to improve the flowability of polyphenylene ether resin compositions, they achieve their object only with a great sacrifice in heat resistance. Also, they were not able to improve the chemical resistance of polyphenylene ether resin compositions.
Meanwhile, propylene polymers have been in general use for the production of molded articles, film, and sheet on account of their outstanding moldability, toughness, water resistance, and chemical resistance, and their low price attributable to their low specific gravity.
Unfortunately, propylene polymers have shortcomings or room for improvement in heat resistance, stiffness, impact resistance, coatability, and adhesion properties. This prevents the development of their new applications. There is an urgent need for improvement particularly in heat resistance and impact resistance.
For this reason, there is a demand for a resin composition composed of polyphenylene ether and a propylene polymer which would exhibit the features of both (i.e., improved moldability and improved impact resistance). It will find uses in new broad application areas.
In practice, however, no satisfactory resin compositions have been obtained from polyphenylene ether and polypropylene mixed together on account of their poor compatibility. It is only possible to obtain a resin composition which gives injection molded articles with phase separation between polyphenylene ether and polypropylene. This phase separation greatly deteriorates the appearance and mechanical properties of the molded articles.
The compatibility of polyphenylene ether with polypropylene may be improved by incorporating polyphenylene ether with a propylene polymer grafted with a styrene monomer, as disclosed in Japanese Patent Laid-open No. 75663/1974. This method, however, does not provide any composition which is superior in both heat resistance and impact resistance.
A resin composition having superior mechanical properties can be obtained by the incorporation of polyphenylene ether with a styrene monomer-grafted propylene polymer and a rubbery substance, as disclosed in Japanese Patent Application No. 33445/1988. However, it gives injection molded products which suffer segregation presumably on account of poor melt-flow characteristics.
Under these circumstances, there has been a strong demand for a composition composed of polyphenylene ether, modified propylene polymer, and rubber substance, said composition having good mechanical properties and giving injection molded articles with a good appearance.
In view of the forgoing, the present inventors carried out extensive studies to develop a new technology. As the result, they succeeded in the production of a new resin composition which is superior in heat resistance, melt-flow characteristics, processability, chemical resistance, appearance, and gloss. This success led to the present invention.